Change the default toolchain used by Rust

The following command will change the default toolchain that Rust uses.

$ rustup default [version]

For example, to use the nightly version of Rust by default, run te following.

$ rustup default nightly

You can confirm that the version has changed by passing the -V flag

$ rustc -V
rustc 1.45.0-nightly (a74d1862d 2020-05-14)